Networks that transmit information by using Ethernet (registered trademark) packets have become widespread. Also, Optical Transport Networks (OTNs) defined in ITU-T Recommendation G.709 are becoming widespread as networks for example large-volume trunk line systems. Thus, transmission equipment that maps Ethernet packets onto OTN frames and transmits the packets has been implemented in practical use. In other words, transmission equipments having the Ethernet over OTN function have been implemented in practical use.
In some cases, networks such as those described above have a redundant configuration in order to enhance their reliability. In Ethernet over OTN for example, a plurality of OTN paths are provided between transmission equipments. Also, transmission equipment includes a switch for selecting an output port (i.e., an OTN path) for Ethernet packets. In such a case, when a failure has occurred in a currently used OTN path, the switch of transmission equipment selects a different OTN path. This configuration makes it possible to continue communications even when a failure has occurred in a currently used system.
As a related technique, a device that selects a transmission path in accordance with a request from a communication system, a router that distributes packets in accordance with the priority of the packets, and the like are known (for example, Japanese Laid-open Patent Publication No. 2008-72181, Japanese Laid-open Patent Publication No. 2002-300193, Japanese Laid-open Patent Publication No. 2001-69166, and Japanese Laid-open Patent Publication No. 2003-338837).
The priority of an Ethernet packet is specified by using a VLAN tag in layer 2 defined by IEEE802.1Q, a TOS (Type Of Service) defined by RFC2474, and the like. For example,
Ethernet packets that transmit audio data or video image data are often given high priority. Further, it is desirable that Ethernet packets with high priority be stored in OTN frames and thereafter be transmitted through an OTN path whose transmission delay is small.
According to the conventional techniques, however, when a failure has been detected in a currently used OTN path, transmission equipment selects an available OTN path without taking the priority of Ethernet packets into consideration. This may sometimes cause a situation where Ethernet packets with a high priority are transmitted through an GIN path whose delay is large. In such a case, there is a possibility that the quality of the audio or video image will deteriorate.
The use of an Ethernet test signal permits the measurement of transmission delays of packets. However, the
Ethernet test signal is transmitted while the transmission of actual data (for example client data) is in a halted state. This means that when the Ethernet test signal is used for measuring a transmission delay, the transmission of actual data may be halted. Accordingly, when, for example, a line has been added after the start of communication services, it is difficult to measure the transmission delay of that added line by using the Ethernet test signal.